(1) Field of the Invention
This invention relates to a method of and apparatus for sampling granular materials for analysis. The method and apparatus may also be applied to constant mass flow feeding of granular materials.
(2) Description of the Prior Art
It is desirable to analyse granular materials, e.g. coal, so as to obtain relevant parameters of the characteristics of the materials such as bulk density, moisture content, ash content and/or elemental composition.
While the techniques of analysis are well-known and accepted, the problem has been, and still is, to convey the granular material past the analysis station(s) without altering or changing any of these parameters.
One method of sampling coal for analysis employs a closed screw conveyor with a sampling tube of substantially constant cross-section. The coal is forced through the sampling tube and is compacted therein with the object of achieving approximately constant bulk density of the coal throughout the length of the tube.
Suitable analysis equipment is utilized to determine one or more of the parameters of the coal, e.g. ash content. This method has a number of serious disadvantages. Firstly, the length of the sampling tube is limited and not suitable to more general methods of coal analysis and to achieving compaction of the coal to approximately constant bulk density. High power consumption is required to drive the coal through the sampling tube and the high loads placed on the coal in directions transverse to the direction of motion of the coal can result in mechanical failure of the sampling tube. Finally, undesirable crushing of the coal is obtained due to its low inherent strength or impact resistance.